ISOLATION OF A CDNA WHOSE EXPRESSION IS MARKEDLY INCREASED IN MALIGNANTLY TRANSFORMED FRTL CELLS AND NEOPLASTIC HUMAN THYROID TISSUES

We have cloned a cDNA whose mRNA levels are increased in malignantly t ransformed rat thyroid FRTL cells (FRTL-Tc cells). We constructed a cD NA library from FRTL-Tc cells in lambda gt10 and screened the cDNAs by differential plaque filter hybridization. Twenty-five thousand clones were screened and one cDNA (C140) was selected which corresponded to a mRNA whose expression was 5.8 times higher in FRTL-Tc cells than in FRTL cells. A 0.8 kb specific C140 mRNA was detected by Northern blot analysis of FRTL-Tc and FRTL mRNAs. The C140 cDNA was sequenced and fo und to encode a protein of 227 amino acids. We have found that C140 mR NA is conserved in human thyroid cells, but it is encoded by a smaller 0.7 kb transcript. C140 mRNA was highly expressed in neoplastic thyro id tissues and weakly in normal thyroid tissues in the same patients. Additionally, we found that C140 mRNA was also increased in the thyroi d tissue of a patient with Graves' disease. These results suggest that C140 expression might be higher in rapidly growing thyroid cells than in normal cells, and might provide a new aspect for the study of thyr oid tumours.